Human T cell hybridomas have been generated which secrete various lymphokines regulating normal B cell maturation. One factor, an IgA specific helper factor, is contrasted to polyclonal B cell differentiation factors. In addition, evidence is provided for the heterogeneity of B cell growth and differentiation factors as well as for the existence of a T cell which is capable of inducing a nonspecific Ig class switch. The aim of this proposal is to better characterize these factors, specifically by direct isolation and comparison of their biochemical properties. Since these factors are produced in small amount, albeit with potent biologic activity, large volumes of hybrid supernatants will be obtained, concentrated by ultrafiltration, and chromatographed (ion exchange and sephadex sizing columns). Supernatants generated in serum free conditions are used to raise antibodies against specific lymphokines in mice (monoclonal Ab) and rabbits (hetero-antibodies). Antibodies are screened for blocking activity in factors assays. Blocking antibodies can be used, bound to sepharose, to affinity purify lymphokines and evaluate receptors for B cell growth and differentiation factors. Another approach to the receptors will be through the use of radiolabelled hybrid supernatants and absorption onto target cells, especially those with documented increased receptor numbers. The factors and/or receptors will be contrasted and evaluated from difference and homolgies. These factors will be of importance in the understanding and/or treatment of some immunodeficiency disorders (common variable immunodeficiency and immunodeficiency with hyper-IgM) as well as chronic lymphocytic leukemia.